Heat transfer device

ABSTRACT

A separation wake zone behind a heat transfer tube in a heat transfer device of a heat exchanger or the like is reduced, whereby a heat transfer action of the heat transfer device can be augmented and a pressure loss thereof can be reduced. The heat transfer device of the heat exchanger has a linear or tubular heat transfer object (T) in heat transfer contact with a heat carrier fluid (A), and a heat transfer fin (F) integrally formed with the heat transfer object for heat transmission therebetween. The heat transfer fin is provided with a guide fin ( 10 ) positioned in vicinity of the heat transfer object, and the guide fin conducts the fluid to the rear of the heat transfer object, thereby reducing the separation wake zone behind the heat transfer object. A position (B) of separation point of the fluid is set to be at an angular position (β) equal to or greater than 90° from a stagnation point (E) on the heat transfer object by setting of an attack angle, configuration, position and dimensional proportion of the guide fin.

This is a nationalization of PCT/JP02/08185 filed Aug. 9, 2002 andpublished in Japanese.

TECHNICAL FIELD

The present invention relates to a heat transfer device, and morespecifically, to such a device provided with a guide fin which acts asmeans for controlling a position of separation of a heat carrier fluid.

TECHNICAL BACKGROUND

In general, a heat exchanger for heating or cooling a fluid is providedwith a heat transfer tube through which a thermal medium fluid to beheated or cooled is circulated, and the heat exchanger is so arrangedthat a heat carrier fluid, such as air, is forcedly moved around thetube. The thermal medium fluid in the tube is cooled or heated by heatexchange with the heat carrier fluid through a tube wall of the tube. Insuch a heat exchanger using gaseous fluid as the heat carrier fluid, aheat transfer performance depends on the thermal resistance of the heatcarrier fluid, such as air, and therefore, fins in a variety of formsare attached to the tubes for increasing the heat transferable contactarea between the tube and the heat carrier fluid and improving the heattransfer performance.

For instance, a high-fin-tube type of heat exchanger which has spiralmetal fins attached to metal tubes and the tubes disposed in a staggeredarrangement or an in-line arrangement, and a fin-tube type orplate-fin-and-tube type of heat exchanger, which is known as a kind ofcompact heat exchanger, are incorporated in thermal medium circuits ofvarious power plants, thermal carrier circuits of air-conditioningsystems, cooling water circuits of various internal combustion engines,and so forth.

The fin-tube type of heat exchanger cools the thermal medium fluid inthe heat transfer tube by heat exchange between the fluid flowingthrough the tube and the gaseous flow moving in an area outside thetube. The fin increases the heat transferable area of the tube so as toimprove the thermal efficiency of heat exchange between the gaseous flowoutside the tube and the fluid inside the tube. In such a fin-tube typeof heat exchanger, a heat exchanger formed with a number of dimples orslits is disclosed in Japanese patent laid-open publication No. 8-291988and so forth.

However, even if the heat transfer effect can be designed to be doubledby improvement of configuration of the fin, the pressure loss in theheat exchanger is caused to greatly increase on the contrary, and itdifficult to overcome such a problem. Therefore, it has been understoodto be difficult to realize both of augmentation of heat transfer andreduction of pressure loss of heat carrier fluid by improving theconfiguration of the fin.

FIG. 10 is a partial cross-sectional view of a heat exchanger which is aconventional plate-fin-and-tube type of air-cooled heat exchanger.

With respect to heat transfer tubes T extending through fins F, an airflow A is compulsorily ventilated in a direction perpendicular to thetubes T, so that the air flow A passes through fluid passages P formedbetween the fins F. The air flow A separates from a boundary surface ofthe tube T at a separation point B, when flowing rearward along theouter surface of the tube T in the passage P between the fins F. Theseparation point B has been considered to reside at a position rearwardfrom a stagnation point E by an angle β, which is approximately 80°.Because of such a separation phenomenon of the air flow A, the air flowA cannot sufficiently enter the rear of the tube T, and this results increation of a separation wake zone C behind the tube T, which is calledas “dead water zone”. The separation wake zone C causes the heattransfer effect of heat exchanger to decline and the pressure lossthereof to increase.

It is a purpose of the present invention to provide a heat transferdevice which can reduce the separation wake zone behind the heattransfer tube so as to improve the heat transfer effect of the heattransfer device in the heat exchanger and so forth, and which can reducethe pressure loss of the heat transfer device.

It is another purpose of the present invention to provide an air-cooledtype of heat exchanger which can decrease a load of a fan for providingcompulsory draft of the heat carrier fluid, thereby reducing noise ofthe heat exchanger during operation of the fan.

It is still another purpose of the present invention to provide aseparation position control method for the heat transfer device whichallows the position of separation point of the heat carrier fluid to becontrolled with use of separation position control means having asimplified arrangement, thereby reducing the separation wake zone behindthe tube.

DISCLOSURE OF THE INVENTION

Having preserved steady efforts to the study for achieving thesepurposes, the present inventor confirmed that the air flow A could enterthe rear of the tube by displacing the position of the aforementionedseparation point B to a range of the angle β>90°, whereby the separationwake zone C could be considerably reduced or eliminated. Thus, thepresent inventor attained this invention, based on such findings.

The present invention provides a heat transfer device having a linear ortubular heat transfer object which is in heat transfer contact with aheat carrier fluid, and a heat transfer fin which is integrally formedwith the heat transfer object for heat transmission between the tube andthe heat transfer object, comprising:

said heat transfer fin provided with a guide fin, which is positioned invicinity of said heat transfer object and oriented at a predeterminedattack angle with respect to said fluid so as to conduct the fluid torear of said heat transfer object, thereby reducing a separation wakezone behind said heat transfer object.

According to the arrangement of the present invention, the heat carrierfluid (A) flows through a fluid passage formed between the guide fin(10) and the heat transfer object (T), while being in heat transfercontact with the object, guide fin and heat transfer fin. The guide finis oriented to make a predetermined attack angle (α) with respect to thefluid, so that the fluid is conducted to the rear of the heat transferobject. The guide fin acts to reduce the separation wake zone (C) behindthe tube, thereby augmenting the heat transfer of the device and also,reducing the pressure loss thereof. A part of the heat carrier fluidgets over or goes beyond the guide fin to generate a longitudinal vortexbehind the guide fin. This longitudinal vortex effect causes a swirlingflow to be generated in the rear of the guide fin, the swirling flowbeing deflected in accordance with the inclination of guide fin (theattack angle α). The swirling flow makes further improvement in the heattransfer effect of the heat transfer device without providing anexcessive pressure loss in the heat transfer device.

The present invention also provides an air-cooled type of heat exchangerprovided with a fan effecting compulsory draft of the heat carrier fluidand said heat transfer device as set forth above, whereby noise causedin operation of the fan is diminished by reduction of pressure loss ofsaid heat transfer device. Since a blast capacity of heat carrier fluidrequired for ensuring a predetermined heat transfer effect is lowered byaugmentation of the heat transfer of the device and reduction of thepressure loss thereof, the load of fan for compulsory draft is reduced.Therefore, it is possible to reduce the electricity consumption of fanand the noise in the air-cooled type of heat exchanger during operationof the fan.

The present invention further provides a method of controlling aposition of separation in a heat transfer device which has a linear ortubular heat transfer object and a heat transfer fin integrally formedwith the heat transfer object for heat transmission between the tube andthe heat transfer object, a heat carrier fluid being passed through afluid passage formed between the heat transfer fins,

wherein a guide fin is disposed in vicinity of said heat transfer objectand a position of a separation point of said fluid with respect to theheat transfer object is controlled to be in a range of angular positionequal to or greater than 90° from a stagnation point (E) of the heattransfer object by setting of an attack angle, configuration, positionand dimensional proportion of the guide fin.

According to this feature of the present invention, the position ofseparation point is determined by setting of the attack angle,configuration, position and dimensional proportion of the guide fin. Theposition of separation point is a principal factor on the basis of whicha manner of creation of separation wake zone behind the heat transferobject is controlled, and the condition of the separation wake zone isone of essential factors on which the heat transfer performance andpressure loss of the heat transfer device or the heat exchanger aredependent. Therefore, in accordance with the method of the presentinvention, the position of separation point is controlled by setting ofthe guide fin so that the separation wake zone behind the heat transferobject is reduced, whereby both of the heat transfer performance and thepressure loss of the heat transfer device or the heat exchanger can beimproved.

In a preferred embodiment of the present invention, an altitude (h) ofthe highest part of the guide fin is dimensionally set to be equal to orgreater than one quarter (¼) of an interval (Pf) of the heat transferfins, and the length (L) of base/the altitude (h) at the highest part ofthe guide fin is set to be in a range from 2 to 7 (2˜7). Preferably, arear end portion of the guide fin is set to be positioned at the angularposition θ₂ (the angle θ₂ measured from the stagnation point E) which isin a range of from 80° to 176° (80°˜176°), and the distance R′ betweenthe rear end portion and the center of the heat transfer object withrespect to the radius R of the heat transfer object is set to be a ratioranging from 1.05 to 2.6 (R′/R=1.05˜2.6).

The guide fin may be provided on either side of the heat transfer fin soas to extend from one side to the other side, or it may be provided onboth sides in a pair. In a case of provision of the guide fin on onlyone side, the altitude (h) at the highest part of guide fin is set tobe, at least, one half of the interval (Pf) of the heat transfer fins.For example, the guide fin has a triangular configuration which includesa base on a plane of the heat transfer fin and an oblique line definingits upper edge, the upper edge inclining from a position of the gaptoward the upstream side of the heat carrier fluid flow. The guide finmay have a trapezoidal, rectangular or arcuate configuration, or thelike. Preferably, the guide fin is integrally formed on the heattransfer fin by cutting and elevating the heat transfer fin.

In a further preferred embodiment of the present invention, theaforementioned heat transfer object is a heat transfer tube (T) throughwhich a thermal medium fluid to be heated or cooled can pass, and theheat transfer fins are arranged in a lengthwise direction of the tube,spaced a predetermined distance from each other. The thermal mediumfluid is cooled or heated by heat exchange between the thermal mediumfluid in the tube and the heat carrier fluid flowing in close vicinityof the surfaces of the tube and the heat transfer fin. The guide finsare positioned on both sides of the tube in symmetry so as to definefluid passages for the heat carrier fluid between the guide fins and thetube. The passage diverges toward the upstream side of the heat carrierfluid and converges toward an area downstream of the tube. The attackangle of the guide fin with respect to a direction of the heat carrierfluid flow is set to be a predetermined angle in a range from 5° to 60°(5°˜60°) and the downstream end of the guide fin is spaced from the tubewall of the heat transfer tube so as to form a narrow gap for spoutingthe heat carrier fluid therethrough to the rear of the tube. Accordingto such a heat transfer device, the heat carrier fluid flows through thefluid passage formed between the tube and the guide fin while being inheat transfer contact with the tube and the heat transfer fin. Thecontiguity is made in a direction of the heat carrier fluid flow by theguide fin and the tube, whereby the separation point of the heat carrierfluid is shifted to a position at an angle β>90° and the velocity ofheat carrier fluid flow is accelerated so as to direct a spouting flowat a relatively high velocity through the aforesaid gap to the rear ofthe tube. The heat carrier fluid flowing into the rear of the tubeprevents so-called “dead water zone” from being created behind the tube,and therefore, the separation wake zone is considerably reduced orsubstantially eliminated. Such reduction or elimination of theseparation wake zone results in not only augmentation of heat transferbetween the tube and the heat carrier fluid, but also reduction ofpressure loss of the heat carrier fluid. In general, the pressure losstends to significantly increase in use of a heat carrier fluid of a lowReynolds number, and therefore, the present invention exhibitsespecially significant effects of heat transfer augmentation andpressure loss reduction in its application to a heat exchanger with useof such a heat carrier fluid.

In the aforementioned method of controlling a position of separation,the guide fins are symmetrically disposed in a direction of span of theheat transfer objects, and the attack angle α of the guide fin relativeto the direction of the heat carrier fluid flow is set to be apredetermined angle in a range of 5°˜60°, preferably 10°˜45°, morepreferably 10°˜30°. The attack angle, configuration, position anddimensional proportion of the guide fin are preferably so set as togenerate a swirl flow behind the guide tube. The position of separationpoint (β) is preferably controlled to be an angular position equal to orgreater than 100° from the stagnation point (E).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of theplate-fin-and-tube type of heat exchanger provided with a guide finaccording to the present invention;

FIG. 2 is an enlarged cross-sectional view of the heat exchanger asshown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view of the heat exchanger takenas an image of water flow which is a simulation of property of air flow,the property of air flow in the conventional heat exchanger without theguide fin being illustrated in FIG. 3(A) and the property of air flow inthe heat exchanger with the guide fin being illustrated in FIG. 3(B);

FIG. 4 is a graphic illustration showing results of experiments onaugmentation of heat transfer and reduction of pressure loss in the heatexchanger provided with the guide fin;

FIG. 5 includes a graphic illustration, layout drawings and table ofdimension ratios which show the other experimental results on effects ofaugmentation of heat transfer and effects of reduction of pressure lossin the heat exchanger provided with the guide fin;

FIG. 6 is a graphic illustration, layout drawings and a table ofdimension ratios which show the other experimental results on effects ofaugmentation of heat transfer and reduction of pressure loss in the heatexchanger provided with the guide fin, an example of the best testresults obtained so far being indicated therein;

FIG. 7 includes a graphic illustration, layout drawings and a table ofdimension ratios which show the other experimental results on effects ofaugmentation of heat transfer and reduction of pressure loss in the heatexchanger provided with the guide fin;

FIG. 8 is a partial cross-sectional view showing an alternative of theguide fin;

FIG. 9 is a partial cross-sectional view showing variations of the guidefin in regard to its configuration and layout; and

FIG. 10 is a partial cross-sectional view showing a conventionalarrangement of a plate-fin-and-tube type air-cooling heat exchanger anda property of air flow therein.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the heat exchanger according to the presentinvention is described in detail hereinafter.

FIGS. 1 and 2 are cross-sectional views showing an embodiment of theplate-fin-and-tube type of heat exchanger.

The heat exchanger has a plurality of heat transfer tubes T spaced aparta predetermined distance from each other and arranged in rows, and aplurality of plate fins F arranged in an orientation perpendicular tothe tubes T. The tube T and the fin F are made of the same sort ofmetal. The tube F constitutes a fluid passage for a thermal medium fluidhaving a circular cross-section, and the fins F on the tubes T areintegrally attached to the tubes T for heat transmission between the finand the tube, so that an extensive area of heat transferable planesurface is provided in the heat exchanger. Fluid passages P, throughwhich a flow of cooling air A can pass, are defined between the fins F.

The thermal medium fluid at a relatively high temperature circulatesthrough the tubes T and the cooling air flow A is forcedly drafted in adirection perpendicular to the tubes T. The air flow A blown through theheat exchanger moves on a boundary layer of the fins F and tubes T as aheat carrier fluid, so as to receive the heat by heat transfer contactwith the fins F and tubes T, and then, the air is exhausted through adownstream exhaust port of the heat exchanger.

The heat exchanger of this embodiment is provided with guide fins 10elevated from the fins F, which act as separation restriction means forrestricting separation of the air flow A. The guide fin 10 is formed bylocally cutting and elevating the fin F in a form of triangle. The fin Fis formed with an opening 11 corresponding to an outline of the guidefin 10. The guide fins 10 are disposed in a pair on both sides of thetube T, and the fins 10 have the formation and layout symmetric withrespect to a center axis of the tube T.

In FIG. 2, an arrangement and a layout of the guide fins 10 areillustrated more concretely.

Each of the guide fins 10 is obliquely oriented at an attack angle αwith respect to a direction of the air flow A. A narrow gap 13 limitedin its fluid passage area by the guide fin 10 is formed between an outersurface of the tube T and a rear end portion 12 of the fin 10. A closepoint 14 opposing against the end portion 12 in a directionperpendicular to the air flow A (a spanwise direction) is spaced adistance S from the end portion 12. The point 14 is positioned at anangle θ₁ measured from a stagnation point E on the tube T. The endportion 12 is positioned at an angle θ₂ (an angle θ₂ measured from thestagnation point E) and a distance R′ in a cylindrical coordinate ofFIG. 2. Preferably, the angle θ₂ is set to be in a range from 80° to176°, and a ratio of the distance R′/a radius R of the heat transfertube is set to be in a range from 1.05 to 2.6, wherein the distance R′is a distance between the end portion 12 and the center of the heattransfer tube.

The fin 10 has a configuration of right-angled triangle with its lengthof the base L and its altitude h. The opening 11 having a profileidentical with that of the fin 10 is adjacent to the base of the fin 10on its side opposite to the tube T. The altitude h (the height of thevertex) is set to be a dimension somewhat smaller than the interval Pfof the fins F (fin pitch). Preferably, the altitude h is set to be adimension equal to or greater than one quarter of the fin pitch Pf, morepreferably, at least one half thereof.

Operation of the aforementioned guide fin 10 is described hereinafter.

The air flow A enters the space between the tube T and the fin 10. Theair flow A gradually accelerates while varying in its direction, as thewidth of the fluid passage between the fin 10 and the tube T reduces inaccordance with the inclination of the fin 10, and the air flow Afinally spouts rearward through the gap 13 at a velocity Vc. The flowspouting through the gap 13 is directed in an approximately tangentialdirection of the point 14.

The guide fin 10 allows the air flow A to be accelerated and stabilized,and also, the fin 10 conducts the air flow A in a direction along asurface of tube wall of the tube T to regulate the direction of spoutingflow through the gap 13. The fin 10, which guides the air flow A, actsto restrict the separation phenomenon of the air flow A from the tube T,so that occurrence of the separation is retarded or delayed. As theresult, a position of the separation point B is displaced considerablyrearward, compared to a case where the guide fin F is not provided. Theangular position β of the separation point B with reference to theposition of the stagnation point E has been observed to be approximately80° in a conventional arrangement without provision of the guide fin 10,whereas the angular position β is observed to be equal to or greaterthan 90°, e.g., 100°˜135°, in the heat exchanger according to thisembodiment. As the result of rearward displacement of the separationpoint B, the air flow A can smoothly flows to the rear of the tube T,and the pressure loss of the air flow A is reduced. Thus, the guide fin10 acts as separation position control means for controlling theposition of the separation point B, so that the separation point B canbe controlled by the configuration and position of the guide fin 10.

Further, the altitude h of the guide fin 10 is set to be smaller thanthe fin pitch Pf, and therefore, a gap G is provided between an upperedge 15 of the fin 10 and the fin F. A part of the air flow A flowsbeyond the fin 10 to the rear thereof to cause a swirl motion, so that alongitudinal vortex is generated behind the fin 10. The fin 10 isoriented in the attack angle α relative to the air flow A and the gap Gextends in an direction of the angle α with respect to the air flow A,and therefore, the longitudinal vortex flow is deflected by the fin 10so as to somewhat get close to the tube T. An effective heat transferaugmentation, e.g., the heat transfer augmentation effect of 15%˜50%,can be attained by generation of the longitudinal vortex, without anexcessive increase of pressure loss being caused.

FIG. 3 shows a captured image of water flow, which is a simulation ofproperty of the air flow A. The air flow property in a heat exchangerwhich does not have the guide fin 10 is illustrated in FIG. 3(A), andthe air flow property in a heat exchanger which has the guide fin 10 isillustrated in FIG. 3(B).

The magnitude of each vector in FIG. 3 represents the velocity of air.As is apparent from comparison between FIG. 3(A) and FIG. 3(B), the deadwater zone behind the tube is considerably reduced by provision of theguide fin 10.

Thus, the gap 13 directs toward the rear of the tube T, the spouting airflow having a relatively high velocity and deviated inward of the tubeT. The spouting air flow dispels a major part of the deadwater zone ofthe tube T so that the separation wake zone C is reduced. This, incooperation with effects of generation of the longitudinal vortex as setforth above, results in improvement of heat transfer performance of theheat exchanger and reduction of pressure loss of the air flow A.

FIG. 4 is a graphic illustration showing results of experiments onaugmentation of the heat transfer and reduction of the pressure loss inthe heat exchanger constructed as set forth above.

The heat exchanger as used in the experiments are provided with the heattransfer tubes T located in a staggered arrangement and the dimensionsof respective parts thereof are set to be as follows:

Diameter of the tube T D = 30 mm Distance between the tubes T W = 75 mmPitch of the plate fins H = 5.6 mm Altitude of the guide fin h = 5 mmDimension of the gap 13 S = 9 mm Attack angle of the guide fin 10 α =15° Angular position of the close point 14 θ₁ = 110°

The present inventor has carried out substantive tests on effects of theheat transfer augmentation and reduction of the pressure loss with useof a first heat exchanger as shown in FIG. 4(A) and a second heatexchanger as shown in FIG. 4(B) with respect to the air flow A in a widerange of flow rate (Reynolds number=300˜2000), wherein the first heatexchanger has the guide fins 10 arranged only on the front-most row ofthe tubes, and the second heat exchanger has the guide fins 10 arrangedon the front-most row and the second row of the tubes. The results oftests on the effects of heat transfer augmentation are shown in FIG.4(C), and the results of tests on the effects of pressure loss reductionare shown in FIG. 4(D), wherein j/j_(GO) in FIG. 4(C) represents theratio (ratio of heat transfer effect) of the transferred heat (j) as ina case of provision of the guide fin 10 relative to the transferred heat(j_(GO)) as in a case of lack of the guide fin 10, and wherein f/f_(GO)in FIG. 4(D) represents the ratio (ratio of pressure loss) of thepressure loss (f) in a case of provision of the guide fin 10 relative tothe pressure loss (f_(GO)) in a case of lack of the guide fin 10.

As shown in FIGS. 4(C) and 4(D), the heat exchanger with the guide fins10 in accordance with the present embodiment exhibits generally improvedheat transfer effects and pressure loss reducing effects over a widerange of flow rate. Especially, significantly improved heat transfereffects and pressure loss reducing effects have been observed in acondition of low Reynolds number. It has been found that, in a conditionof Reynolds number=300˜400, the ratio of heat transfer effect j/j_(GO)reaches approximately 1.3 and the ratio of pressure loss reducing effectf/f_(GO) is reduced to be approximately 0.45.

FIGS. 5 through 7 are graphic illustrations, layout drawings and tablesof dimension ratios, which show the other test results on effects ofaugmentation of heat transfer and effects of reduction of pressure lossin the heat exchanger constructed as set forth above.

The heat exchanger, the test results of which are shown in FIG. 5, hasthe guide fins 10 provided only on the front-most row (upstream-mostrow) in an in-line arrangement (FIG. 5(B)). The heat exchanger, the testresults of which are shown in FIG. 6, has the guide fins 10 providedonly on the front-most row (upstream-most row) of the tubes, the tubes Tbeing disposed in a staggered arrangement (FIG. 6(B)). Further, the heatexchanger, the test results of which are shown in FIG. 7, has the guidefins 10 provided on respective rows of the tubes, the tubes T beingdisposed in an in line arrangement (FIG. 7(B)). FIG. 6 exemplifies oneof the most favorable results in those obtained so far.

In FIGS. 5(A), 6(A) and 7(A), there are shown ratios of dimensions ofthe respective parts in each of the heat exchangers as illustrated inFIGS. 5(C); (D), 6(C); (D) and 7(C); (D).

Having compared a case of provision of the guide fin 10 in thefront-most row of the tubes T with a case of lack of the guide fins 10,the ratio of heat transfer effect j/j_(GO) exhibits approximately1.1˜1.3 and the ratio of pressure loss reducing effect f/f_(GO) exhibitsapproximately 0.45˜0.9, as shown in the graphic diagrams of FIG. 5(A)and FIG. 6(A).

On the other hand, the ratio of heat transfer effect j/j_(GO) and theratio of pressure loss reducing effect f/f_(GO) do not necessarilyexhibit favorable results even if the guide fins 10 are provided formore tubes T. For instance, the ratio of heat transfer effect j/j_(GO)and the ratio of pressure loss reducing effect f/f_(GO) result inundesirable values on the contrary, as shown in the graphic diagram ofFIG. 7(A). Therefore, the guide fins 10 are, if desired, provided onlyfor the front-most row of the tubes T, for every two rows thereof, orfor the rows spaced a few rows.

FIGS. 8 and 9 are cross-sectional views showing alternatives of theguide fins 10.

The guide fins 10 may be cut and bent on one side of the fin F as shownin FIG. 8(A), or may be cut and bent on both sides of the fin F as shownin FIG. 8(B).

Further, the configuration of each of the guide fins 10 are not limitedto the right-angled triangle, but it may have an outline, such as a formof trapezoid, rectangle, triangle or arc, so far as it includes an upperedge 15 in a form of straight line or curved line gradually increasingin its height in a direction of the air flow A, as illustrated in FIGS.9(A)˜9(E).

Furthermore, the guide fins 10 may be positioned on upper and lower finsF in a pair so as to oppose against each other, as shown in FIG. 9(F).

In addition, the guide fin 10 may be elevated from the fin Fperpendicularly or inclined at a predetermined angle, as shown in FIGS.9(G)˜9(I).

Noise reduction effects obtained in the heat exchanger with the guidefins 10 as set forth above is further described hereinafter.

In general, a fin-tube type heat exchanger is provided with a fan forcompulsory draft of air through the fluid passage P between the fins F Acapacity of the fan is to be substantially determined in accordance withthe air flow rate and the pressure loss.

A specific noise level of the fan (a maximum efficiency point) L_(SA) isgenerally indicated by the following formula:L _(SA)[dB(A)]=L _(A)−10×log QPr²wherein

-   L_(SA): Specific Noise Level [dB(A)],-   L_(A): Noise Level [dB(A)],-   Q: Air Flow Rate [m³/min],    and Pr: Pressure Loss (Total Pressure) [mmAq].

Having examined the noise reduction effects of the heat exchanger on thebasis of the test results as shown in FIG. 4, the ratio of heat transferperformance j/j_(GO) is approximately 1.3 (FIG. 4(C)) and the ratio ofpressure loss reduction effect f/f_(GO) is 0.45 (FIG. 4(D)), if theReynolds number Re is 350. Having reviewed improvement of the heattransfer performance, the flow rate is reduced relatively to theidentical heat transfer performance. Therefore, a noise reduction effectcan be obtained in association with reduction of the air flow rate.

However, taking into consideration effects of the longitudinal vortexgenerated by the guide fin 10, noise enlargement effect due to thelongitudinal vortex may be also supposed to occur. Therefore, assumingthat the pressure loss is merely reduced regardless of whether the airflow rate is reduced by improvement of the heat transfer effect, it canbe deemed that the pressure loss is simply reduced to 45%(f/f_(GO)=0.45). Therefore, provided that the flow rate Q is constant,the reduction effect of the noise level ΔL_(A) can be obtained on thebasis of the formula for specific noise level and the above conditions,as follows:

$\begin{matrix}{{\Delta\; L_{A}} = {{10 \times \log\mspace{14mu}\Pr^{2}} = {20 \times \log\mspace{14mu}\Pr}}} \\{= {{20 \times {\log\left( {f/f_{G0}} \right)}} = {{- 20} \times {\log\left( {f_{G0}/f} \right)}}}} \\{= {{{- 20} \times {\log\left( {1/0.45} \right)}} = {{- 7}\mspace{14mu}{dB}}}}\end{matrix}$

Similarly, in the results of tests as shown in FIG. 4, the effect ofpressure loss reduction is f/f_(GO)=0.66 in a case of the Reynoldsnumber Re=2000. The reduction effect of noise level ΔL_(A) can besimilarly obtained, based on the following equation:ΔL _(A)=−20×log(1/0.66)=−3.6 dB

Thus, according to a forced convection type of heat exchanger providedwith the guide fins 10 arranged as set forth above, the noise level canbe lowered by approximately 4 dB˜7 dB over a wide range of the air flowrate (Reynolds number=300˜2000), without deterioration of the heattransfer performance. In general, the fin-tube types of heat exchangersare used as air-cooled type of cooling devices for air conditioningmachines or the like, and problems of fan noise are raised often.However, the load of fan can be reduced and the noise caused inoperation of the fan can be considerably lowered, according to the heatexchanger with the aforementioned arrangements.

Although the present invention has been described as to specificpreferred embodiments, the present invention is not limited to suchembodiments, but may be modified or changed without departing from thescope of the invention as defined in the attached claims.

For instance, the heat exchanger of the aforementioned embodiment is soarranged that the heat carrier fluid at a high temperature is circulatedthrough the heat transfer tubes T and that the cooling air flow ispassed through the fluid passages P, but the kinds of fluids and thetemperatures thereof are arbitrary. For example, the heat carrier fluidat a low temperature may be circulated through the heat transfer tubes Tand the air flow at a high temperature may be passed through the fluidpassages P.

Further, any of fluids can be used as the heat carrier fluid circulatingthrough the tubes T and the heat carrier fluid passing through thepassage P.

Furthermore, the cross-section of the tube T is not limited to thecircular section, but may be a square section, elongated round section,ellipse section, or the like.

This invention can be also applied to any type of heat transfer devicewhich comprises a linear heat transmission member in heat transferablecontact with a heat carrier fluid and a plane heat transfer finintegrally formed with the heat transmission member for heattransmission between the fin and the member.

INDUSTRIAL APPLICABILITY

As described above, a heat transfer device can be provided, which canreduce the separation wake zone behind the heat transfer tube, therebyimproving the heat transfer effect of the heat transfer device in theheat exchanger and so forth, and which can reduce the pressure loss ofthe heat transfer device, in accordance with the present invention.

Further, an air-cooled type of heat exchanger can be provided, which candecrease a load of a fan for providing compulsory draft of the heatcarrier fluid, thereby reducing noise of the heat exchanger duringoperation of the fan, in accordance with the invention.

Furthermore, according to a separation point control method of thepresent invention, the position of separation point of the heat carrierfluid can be controlled with use of separation position control meanshaving a simplified arrangement, whereby the separation wake zone behindthe tube can be reduced.

1. A heat transfer device having linear or tubular heat transfer objectswhich are in heat transfer contact with a heat carrier fluid, and heattransfer fins which are integrally formed with the heat transfer objectfor heat transmission therebetween, the heat transfer object having acircular cross-section, comprising: a pair of guide fins positioned onboth sides of said heat transfer object in the vicinity of the heattransfer object, the guide fins being configured for delaying a positionof separation of the heat carrier fluid, an upstream end of the guidefin being located on an upstream side of a center of the heat transferobject, a downstream end of the guide fin being located on a downstreamside of the center, each of said guide fins having an upper edge in theform of a straight line or curved line gradually increasing in height ina direction of flow of said heat carrier fluid for generating alongitudinal vortex behind the guide fin, each of the guide fins havinga base on a plane of said heat transfer fin and being oriented at anattack angle α in a range from 10° to 60° relative to the direction offlow of said fluid to define a fluid passage for the heat carrier fluidbetween the guide fin and the heat transfer object, the passagediverging toward an upstream side of the heat transfer object andconverging toward a downstream side of the heat transfer object, analtitude (h) at a highest part of the guide fin being dimensionally setto be equal to or greater than one half of an interval (Pf) of said heattransfer fins, a length (L) of said base being greater than a radius (R)of the heat transfer object, a ratio of the length (L) the base to thealtitude (h) at a highest part of the guide fin being set to be in arange from 2 to 7, the downstream end of the guide fin being spaced fromthe heat transfer object to form a narrow gap for spouting the heatcarrier fluid therethrough, so that said fluid entering an area betweensaid heat transfer objects is accelerated between the heat transferobject and said guide fin and conducted to the rear of said heattransfer object for reducing a separation wake zone behind said heattransfer object and generating, behind the guide fin, a swirl flowdeflected in accordance with an obliquity of said guide fin.
 2. A heattransfer device as defined in claim 1, wherein, in relation to theradius R of said heat transfer object, a ratio of a distance R′ betweensaid downstream end and the center of said heat transfer object is setto be in a range of R′/R=1.05˜2.6.
 3. A heat transfer device as definedin claim 1, wherein said heat transfer object is a heat transfer tubethrough which a thermal medium fluid to be heated or cooled can becirculated, and said heat transfer fins are arranged in a lengthwisedirection of the tube, spaced a predetermined distance from each other,so that the thermal medium fluid is cooled or heated by heat exchangebetween the thermal medium fluid in the tube and the heat carrier fluidflowing in close vicinity of the surfaces of the tube and the heattransfer fin; and wherein said guide fins are positioned symmetricallywith respect to the tube.
 4. A heat transfer device as defined in claim1, wherein said guide fin has a triangular configuration which includesthe base on the plane of said heat transfer fin.
 5. An air-cooled typeof heat exchanger comprising said heat transfer device as defined inclaim 1, and a fan effecting compulsory draft of the heat carrier fluid,whereby noise caused in operation of the fan is diminished by reductionof pressure loss of said heat transfer device.
 6. A method ofcontrolling a position of separation in a heat transfer device which haslinear or tubular heat transfer objects and heat transfer finsintegrally formed with the heat transfer object for heat transmissiontherebetween, the heat transfer object having a circular cross-section,a heat carrier fluid being passed through a fluid passage formed betweenthe heat transfer fins, comprising the steps of: disposing a pair ofguide fins on both sides of said heat transfer object in the vicinity ofsaid heat transfer object to generate longitudinal vortices behind saidguide fins, the guide fins being configured for delaying a position ofseparation of the heat carrier fluid, an upstream end of the guide finbeing located on an upstream side of a center of the heat transferobject, a downstream end of the guide fin being located on a downstreamside of the center, each of said guide fins having an upper edge in aform of a straight or curved line gradually increasing in its height ina direction of flow of said heat carrier fluid for generating alongitudinal vortex behind the guide fin, each of the guide fins havinga base on a plane of said heat transfer fin and being oriented at anattack angle α in a range from 10° to 60° relative to a direction offlow of said fluid to define a fluid passage for the heat carrier fluidbetween the guide fin and the heat transfer object, the passagediverging toward an upstream side of the heat transfer object andconverging toward a downstream side of the heat transfer object, analtitude (h) at a highest part of the guide fin being dimensionally setto be equal to or greater than one half of an interval (Pf) of said heattransfer fins, a length (L) of said base being greater than a radius (R)of the heat transfer object, a ratio of the length (L) the base to thealtitude (h) at a highest part of the guide fin being set to be in arange from 2 to 7, the downstream end of the guide fin being spaced fromthe heat transfer object to form a narrow gap for spouting the heatcarrier fluid therethrough, and controlling a position (β) of aseparation point of said fluid with respect to the heat transfer objectto be in a range of angular position equal to or greater than 90° from astagnation point (E) on the heat transfer object by setting of an attackangle, configuration, position and dimensional proportion of the guidefin so that a swirl flow is generated behind said guide fin and thatsaid fluid entering an area between said heat transfer object and theguide fin is accelerated therebetween and conducted to the rear of theheat transfer object.
 7. A method according to claim 6, wherein in thedisposing step, said guide fins are disposed in a direction of span ofthe heat transfer objects in symmetry and the attack angle (α) of saidguide fin to a direction of flow of said heat carrier fluid is set to bea predetermined angle in a range from 10° to 60°.
 8. A method accordingto claim 6, wherein in the controlling step, the attack angle,configuration, position and dimensional proportion of said guide fin areso set as to generate said swirl flow deviating behind the guide fin inaccordance with an obliquity of said guide fin.
 9. A method according toclaim 6, wherein said heat carrier fluid gradually accelerates whilevarying in its direction, as a width of a fluid passage graduallyreduces between said heat transfer object and said guide fin inaccordance with an obliquity of the guide fin; said heat carrier fluidspouts rearward through a narrow gap (13) for spouting said fluid to therear of the heat transfer object; and a spouting flow through the gap isdirected in a tangential direction of a close point (14) of the heattransfer object which opposes against the downstream end (12) of theguide fin.
 10. A method according to claim 6, wherein in the controllingstep, the position (β) of the separation point (B) is an angularposition of the separation point with reference to said stagnation point(E) occurring at a position ranging from 100° to 135° with respect tothe heat transfer object.
 11. A method according to claim 6, wherein inthe disposing step, said heat transfer objects are located in one of astaggered arrangement and an in-line arrangement, and said guide finsare provided only for a front-most row of said heat transfer objects.12. A method according to claim 6, wherein in the disposing step, saidheat transfer objects are located in one of a staggered arrangement andan in-line arrangement, and said guide fins are provided only for everytwo rows of said heat transfer objects, or for rows spaced a few rowsthereof.
 13. A heat transfer device having heat transfer tubes which arein heat transfer contact with a heat carrier fluid, and heat transferfins which are integrally formed with the tubes for heat transmissiontherebetween, the tube having a circular cross-section, comprising:guide fins positioned on both sides of the tube, the guide fins beingconfigured for delaying a position of separation of the heat carrierfluid, an upstream end of the guide fins being located on an upstreamside of a center of the heat transfer object, a downstream end of theguide fins being located on a downstream side of the center, each ofsaid guide fins having a triangular configuration which includes a baseon a plane of said heat transfer fin and an upper straight edgegradually increasing in height in a direction of flow of said heatcarrier fluid for generating a longitudinal vortex behind the guide fin,each of the guide fins being oriented at an attach angle of a in a rangefrom 10° to 60° relative to a direction of flow of said fluid to definea fluid passage for the heat carrier fluid between the guide fin and thetube, the passage diverging toward an upstream side of the tube andconverging toward a downstream side of the tube, a downstream end of theguide fin being spaced from a tube wall of the heat transfer tube toform a narrow gap for spouting the heat carrier fluid therethrough,wherein a close point located on said tube opposing against a rear endportion of the guide fin in a direction perpendicular to said heatcarrier fluid is spaced a distance (S) from the rear end portion, analtitude (h) at a highest part of the guide fin being dimensionally setto be equal to or greater than one half of an interval (Pf) of said heattransfer fins, a length (L) of said base being greater than a radius (R)of the heat transfer object, and a ratio of the length (L) f the base tothe altitude (h) at a highest part of the guide fin being set to be in arange from 2 to
 7. 14. A heat transfer device as defined in claim 13,wherein said guide fins are positioned symmetrically with respect to thetube.